The present invention relates to a bag for packing, for example, an oxygen scavenger composed of an oxygen adsorbing substance, a carbon dioxide release agent composed of a substance capable of releasing carbon dioxide, a moisture absorbent agent composed of a moisture absorbent substance such as calcium oxide or silica gel, a fragrance preparation including wood powder or the like, a cosmetic powder, a carbon dioxide adsorbent, active carbon, iron powder, paulownia wood ash, zeolite or a highly water absorbent polymer. Further, the present invention relates to a method of producing the above packing bag and a method of producing a film having holes for constituting the packing bag.
The packing bags of the above kind must be permeable for gases. Therefore, and in order to cause them to have a certain level of strength, it is common practice to compose them of materials such as a laminate of porous films having micropores or, as shown in FIG. 1, a double layer or triple layer structure comprising any of paper, nonwoven fabric, cloth cotton, etc. (1) sandwiched by porous film (2) and/or (3).
The porous film is generally obtained by thrusting heated needles through a film or spot-wise irradiating a film with laser to thereby attain perforation. In this perforation, no protrusion is formed across the film section (in the direction of the film thickness), and, because the film is passed through compression rolls at the step of combining with, for example, paper for lamination, the surface of the packing bag is smoothed. Moreover, in the method using heated needles, it is likely for the pore configuration to become nonuniform and diversified.
The conventional packing bags have a drawback, at the time of powder filling, such that, the lower the specific gravity of the powder, the greater the disadvantages such as soaring to an extent that filling is difficult, sticking of powder to seal portion to thereby deteriorate the seal strength and environmental pollution by powder soaring.
The object of the present invention is to provide a bag for packing powder which enables solving these problems, a method of producing the same and a method of producing a film having holes for constituting the packing bag.
The present invention relates to a bag for packing powder, which is characterized by being permeable for gases and comprising a plurality of inwards protrudent hole-forming portions.
In the use of the above packing bag of the present invention, the soaring of powder at the time of filling is inhibited by the protrudent hole-forming portions to thereby avoid soaring problems.
In the present invention, preferably, the packing bag comprises a film (B) having holes provided with protrudent hole-forming portions, the height (h) of the protrudent hole-forming portions being in the range of 2 to 200, still preferably 5 to 100, times the thickness (d) of the film (B) having holes.
Further, the present invention relates to a method of producing a film (B) having holes provided with protrudent hole-forming portions, the film (B) having holes used in the production of the above packing bag, which method comprises the steps of:
disposing a resin film on a metallic cylinder or porous plate furnished with a plurality of openings, and
applying a negative pressure suction to the resin film from a back of the metallic cylinder or porous plate, while heating the resin film at its softening point or higher, so that the resin film at the openings is drawn, toward the back of the metallic cylinder or porous plate to thereby provide protrudent hole-forming portions.
In the present invention, it is preferred that the above resin film comprise a plurality of resin layers different from each other, the resin of an outermost layer having a melting point which is at least 5xc2x0 C. lower than those of other resin layers.
Still further, the present invention relates to a method of producing a bag for packing powder, which method comprising the steps of:
using a composite sheet, which is obtained by laminating the film (B) having holes obtained by the above method with any of paper, cloth cotton or a minutely perforated film (A), and
forming said composite sheet into a bag in such a manner that the protrudent hole-forming portions of the film (B) having holes are directed inwards.
Moreover, the present invention relates to a bag for packing powder produced by using a composite sheet, which is obtained by laminating the film (B) having holes Obtained by the above method with any of paper, cloth cotton or a minutely perforated film (A), and forming said composite sheet into a bag in such a manner that the protrudent hole-forming portions of the film (B) having holes are directed inwards.
In a preferred embodiment of the present invention, the bag for packing powder is one produced by using a composite sheet of triple layer structure, which is obtained by disposing the film (B) having holes obtained by the above method, arranged inside, and a minutely perforated film (A), arranged outside, and interposing paper or cloth cotton therebetween, and forming the composite sheet into a bag in such a manner that the protrudent hole-forming portions of the film (B) having holes are directed inwards.
Furthermore, according to the present invention, there is provided a bag for packing powder produced by using a composite sheet of triple layer structure, which is obtained by laminating the film (B) having holes obtained by the above method with both sides of any of paper, cloth cotton and a minutely perforated film (A), and forming the composite sheet into a bag.